1. Field of the Invention
The present invention relates to a method for generating a basic template utilized to form a screening mask, and more particularly, to a method for generating a basic template according to a specific outputting device, such as a laser printer.
2. Description of the Prior Art
To express natural continuous tones through digital techniques in order to make outputs of a digital printer close to the colors of its inputting device, a general technique called halftone represents darker colors in an image by many color points or a larger color point, and represents lighter colors by fewer color points or a smaller color point. The halftone technique utilizes distribution or size of color points to create visual color variations, and its implementations roughly comprise screening, error diffusion and direct binary search, wherein screening is the most popular technique in the printing industry since the complexity of the screening technique is lower than the other techniques.
The screening technique processes an image to be printed by separately comparing and transferring each part of the image to a gray level of a printing device (such as a digital laser printer) through a mask. For example, a digital laser printer can select a pixel from a continuous tone image to be printed by using a mask, compare the tone of the pixel with a plurality of thresholds to transfer the tone to a gray level established inside the printer, and then dispose color points having the same size at different distances according to an algorithm in order to represent the gray level. In this way, the tones of an output halftone image of the printer can be equal to those of the continuous tone image.
The major objective of the mask is therefore to make the color points vary uniformly and to make the output halftone image of the printer represent a continuous tone image faithfully. However, the image performance directly and significantly relates to the efficiency of the printer. For example, when the resolution of the printer is high, the size of the color point utilized by the printer is small, and hence the image that the printer can present is sophisticated. But when the resolution is not high or the absorbability of carbon powders is not good, small color points cannot be output normally, and the final printing quality will be influenced due to dropping of the carbon powders. This shows that a mask suitable for one specific printer may not be suitable for another printer. However, the mask generally utilized in the printer is designed by the manufacturer, and is not optimized according to each printer, therefore the printing quality cannot be guaranteed.